MODAL TEST OF JONES,JOHN,PAUL (DDG-53) MAST AND MAST-MOUNTED ANTENNAS

A modal test of the John Paul Jones (DDG-53) mainmast structure and ma st-mounted antennas was conducted. The test was part of a larger effor t to accurately determine dynamic characteristics of the ''as-built'' mast/antenna system and survivability in the vibration and underwater explosion (UNDEX) shock environment. Previous mathematical analysis of the DDG-51 class mast and antennas predicted response acceleration le vels during a shock trials scenario to be excessive in some areas. The modal test results now provide, however, confirmed dynamic response c haracteristics including mode shapes, frequencies, and damping for the structure. The test data accounts for the flexibility of ship's struc ture including the deckhouse supporting the mast. In addition, the nat ural frequencies of the antennas were determined for the response rang e of the mast structure with the flexibility of the supporting foundat ions taken into account. Using the test results, a finite element mode l of the mast structure and antennas was built accurately representing the dynamic characteristics of the system. Dynamic transient shock an alysis was conducted to provide response predictions of the mast and a ntennas using the validated model. Any potential response amplificatio n conditions that might result in failure during shock trials were ide ntified.